One of the conventionally-known communication systems, in the fields of mobile communication, is adapted to divide a communication signal into short sections each named “slot” to control, with respect to each slot, the transmission power of the communication signal, and is exemplified by a CDMA system. This system encounters a problem that a mobile terminal far from a base station cannot perform communication with the base station without being interfered by other mobile terminal which is near the base station, resulting from the fact that the communication signals from the mobile terminals are multiplexed in the same frequency band. In order to solve the above-mentioned problem, the CDMA system employs a technology for controlling the transmission power of the mobile terminal in units of the slot with high speed.
FIG. 11 is a schematic diagram showing a frame format of an uplink (transmission from the mobile terminal to the base station) of a W-CDMA system known as one example of the CDMA system. In this system, a frame is defined as a communication unit, has a length of 10 ms, and constituted by 15 slots #0 to #14, each of which has a length of 667 μs, and is multiplexed with DPDCH indicating a data channel for transmitting user data and DPCCH indicating a control channel for transmitting control information. The DPCCH includes a pilot signal as a reference signal, TFCI having transmission format information, FBI having feedback information, and TPC indicating an instruction necessary to control the transmission power.
The TPC of the uplink indicates an instruction necessary to control the transmission power from the mobile terminal to the base station. On the other hand, each slot of a frame of a downlink (transmission from the base station to the mobile terminal) includes TPC indicating an instruction necessary to control the transmission power from the base station to the mobile terminal. The transmission power of the mobile terminal is controlled with respect to each slot on the basis of the TPC of the downlink.
The function designed to control the transmission power of the mobile terminal from the base station is described as “Closed Loop Power Control” (hereinafter simply referred to as “CLPC”) or “Inner Loop Power Control”. According to the CLPC, the base station receives a signal from the mobile terminal to measure the signal, instructs the mobile terminal to increase or decrease the transmission power on the basis of the measurement result, and controls the transmission power of the mobile terminal to increase or decrease the signal in response to the instruction. Additionally, the transmission power is increased or decreased in increments of a step size defined as the difference between transmission powers of slots adjacent to each other, and outputted from the base station to the mobile terminal.
In other words, in response to an instruction indicated by the TPC from the base station, the mobile terminal increases or decreases, with respect to each slot of the uplink, the transmission power by a step size set by the base station, and outputs a signal using the increased or decreased transmission power.
A conventionally-known test device conducts a test on the CLPC function of the above-mentioned mobile terminal. FIG. 12 is a block diagram showing a signal analyzer having a function the same as the feature of the conventional mobile terminal test device.
The signal analyzer 1 is shown in FIG. 12 and comprises a connecting terminal 1a, a directional coupler 2, a power control setting section 3, a control section 4, a transmitting section 5, a receiving section 6, an analyzing section 7, a judging section 8, a display control section 9, and a display section 10. The transmitting section 5 has a power control request section 5a and a transmitting circuit 5b. The receiving section 6 has a receiving circuit 6a, an analog-to-digital (A/D) converter 6b, and a memory section 6c. The analyzing section 7 has a slot detecting section 7a, a slot power detecting section 7b, and an analysis result memory section 7c. 
The connecting terminal 1a is connected to a mobile terminal 11 identified as a test object through a coaxial cable, and connected to the transmitting circuit 5b and the receiving circuit 6a through the directional coupler 2.
The power control setting section 3 is adapted to set, to the power control request section 5a through the control section 4, information on the number of slots of a signal to be transmitted from the mobile terminal 11, whether to have the transmission power increase or decrease, a step size and the like. And the power control setting section 3 is adapted to instruct to start and stop the test.
The control section 4 is adapted to control, to the power control request section 5a on the basis of the information from the power control setting section 3, information on the number of slots of a signal to be transmitted from the mobile terminal 11, whether to have the transmission power increase or decrease, a step size and the like. Further, the control section 4 is adapted to output, to the slot detecting section 7a of the analyzing section 7, a signal to instruct the slot detecting section 7a to start the measurement of the transmission power of each slot in response to the instruction from the power control setting section 3, and to output a signal to instruct the slot detecting section 7a to terminate the measurement of the transmission power of each slot after a specific period of time.
The power control request section 5a is adapted to output, to the transmitting circuit 5b, a transmission request signal corresponding to the information on the number of slots of a signal to be transmitted from the mobile terminal 11, whether to have the transmission power increase or decrease, a step size and the like. And the power control request section 5a is adapted to output a trigger signal to the slot detecting section 7a of the analyzing section 7 when outputting the transmission request signal to the transmitting circuit 5b. 
In response to the transmission request signal from the power control request section 5a controlled by the control section 4, the transmitting circuit 5b is adapted to output, to the mobile terminal 11 through the directional coupler 2 and the connecting terminal 1a, control information corresponding to the transmission request signal from the power control request section 5a. In response to the control information from the transmitting circuit 5b, the mobile terminal 11 outputs a signal using the transmission power corresponding to the control information from the transmitting circuit 5b, while controlling the transmission power with respect to each slot.
The receiving circuit 6a of the receiving section 6 is adapted to receive the signal from the mobile terminal 11 through the connecting terminal 1a and the directional coupler 2, and to output the received signal to the A/D converter 6b. Additionally, the reception frequency of the receiving circuit 6a is controlled by the control section 4, and the same as the carrier frequency of the signal to be outputted by the mobile terminal 11.
The A/D converter 6b converts the signal received from the mobile terminal 11 into a digital signal, and outputs waveform data indicative of the signal from the mobile terminal 11 to the memory section 6c. In response to a start signal from the control section 4, the A/D converter 6b starts to store the waveform data in the memory section 6c, and continues to store the waveform data in the memory section 6c until receiving an end signal from the control section 4. Additionally, the memory section 6c has a writing function and a reading function, and can execute two functions independently.
The analyzing section 7 is adapted to read out the waveform data from the memory section 6c to analyze the waveform data. The analyzing section 7 is constituted by a digital signal processor, and has a slot detecting section 7a, a slot power detecting section 7b, and an analysis result memory section 7c. 
The slot detecting section 7a is adapted to read out, in the first-in first-out order, waveform data from the memory section 6c in response to the trigger signal from the power control request section 5a, and to detect the number of slots from the waveform data read from the memory section 6c. Here, the horizontal axis of the waveform data is a time scale (address in the memory section), while the vertical axis of the waveform data is a voltage scale (value in the memory section). On the other hand, the horizontal axis may be a power scale based on the conversion of voltage to transmission power.
The slot power detecting section 7b is adapted to calculate power values of slots detected by the slot detecting section 7a, and adapted to calculate, as amount of change (relative quantity), the difference between a power value of each slot and a power value of a slot separated from each slot by a specified number of slots.
The analysis result memory section 7c has, as analysis results, the number of slots detected by the slot detecting section 7a, the power value calculated with respect to each slot by the slot power detecting section 7b, and the difference (ratio) between power values of slots separated from each other.
The judging section 8 is adapted to check the operation of the mobile terminal 11 through steps of comparing data stored in the power control request section 5a with data stored in the analysis result memory section 7c, and judging whether or not the mobile terminal 11 identified as a test object is functioning properly. More specifically, the judging section 8 is adapted to judge, in each of slots stored in the analysis result memory section 7c, whether or not the variation in transmission power between slots (relative quantity) is within an allowable error range based on the set step size. For example, under the condition that the set step size is 1 dB and the allowable error range is ±0.5 dB, when the different in transmission power between the relevant slot and the previous slot is 0.8 dB, the relevant slot is judged as a regular slot. When the different in transmission power between the relevant slot and the previous slot is 1.7 dB, the relevant slot is judged as an irregular slot.
The display control section 9 is adapted to produce display data necessary to display a graph showing time-series power levels related to slots and stored in the analysis result memory section 7c, and to display the graph on the display section 10. Additionally, the display control section 9 may be adapted to display the graph on the display section 10 together with the judgments made by the judging section 8 as needed basis.
FIG. 13 is a diagram showing a sequence between the signal analyzer 1 and the mobile terminal 11, the sequence explaining about the test of the above-mentioned CLPC function. The sequence will become apparent through the symbols (a) to (j) shown in FIG. 13. Additionally, in the test of the CLPC function, the signal analyzer 1 sets the step size of the mobile terminal 11 to 1 dB, 2 dB, and 3 dB in that order, and measures, with respect to each step size, the transmission power of a signal from the mobile terminal 11 when controlling the transmission power of the mobile terminal 11.
In step (a), the signal analyzer 1 performs communication with the mobile terminal 11 through the coaxial cable, establishes connection with the mobile terminal 11, and sets the step size as default. In step (b), the signal analyzer 1 instructs the mobile terminal 11 to start the test of the CLPC function. The signal analyzer 1 may conduct other test in steps (a) to (b), and may change the step size in steps (a) to (b).
In step (c), the signal analyzer 1 controls the mobile terminal 11 to set the transmission power of the mobile terminal 11 to a maximum value based on the CLPC measurement. Additionally, the step size of the mobile terminal 11 is 2 dB in step (c) of FIG. 12.
In the test of the CLPC function, the signal analyzer 1 increases the step size of the mobile terminal 11 in increments of 1 dB, 2 dB and 3 dB, and measures the transmission power of each slot with respect to each step size. Therefore, the signal analyzer 1 firstly sets the step size of the mobile terminal to 1 dB in step (d).
In step (e), the signal analyzer 1 controls the mobile terminal 11 to change the transmission power of the mobile terminal 11 from the maximum value based on the CLPC measurement to the minimum value based on the CLPC measurement in increments of 1 dB, and then change the transmission power of the mobile terminal 11 from the minimum value to the maximum value in increments of 1 dB. And the signal analyzer 1 receives a signal from the controlled mobile terminal 11, measures the transmission power of the signal with respect to each slot, and terminates the measurement of the transmission power.
In step (f), the signal analyzer 1 sets the step size of the mobile terminal 11 to 2 dB. In step (g) similar to step (e), the signal analyzer 1 controls the mobile terminal 11 to decrease the transmission power of the mobile terminal 11 from the maximum value based on the CLPC measurement to the minimum value based on the CLPC measurement in increments of 2 dB, and then increase the transmission power of the mobile terminal 11 from the minimum value to the maximum value in increments of 2 dB. And the signal analyzer 1 measures the transmission power of the signal with respect to each slot.
In step (h), the signal analyzer 1 sets the step size of the mobile terminal 11 to 3 dB. In step (i) similar to steps (e) and (g), the signal analyzer 1 controls the mobile terminal 11 to decrease the transmission power of the mobile terminal 11 from the maximum value based on the CLPC measurement to the minimum value based on the CLPC measurement in increments of 3 dB, and then increase the transmission power of the mobile terminal 11 from the minimum value to the maximum value in increments of 3 dB. And the signal analyzer 1 measures the transmission power of the signal with respect to each slot.
After terminating the measurement of the transmission power of each slot, the signal analyzer 1 displays a graph showing the transmission powers measured with respect to each slot and ordered in time in step (j).
FIG. 14 is a sequence diagram explaining in more detail about steps (e), (g), and (i) which are shown in FIG. 13, and in which the signal analyzer 1 controls the mobile terminal 11 to decrease the transmission power of the mobile terminal 11 from the maximum value based on the CLPC measurement to the minimum value based on the CLPC measurement, and then increasing the transmission power of the mobile terminal 11 from the minimum value to the maximum value. The following description is directed to steps (k) to (w).
In step (k), the mobile terminal 11 transmits a signal using the transmission power “Pue” set to the maximum value “Pmax” based on the CLPC measurement while being controlled by the signal analyzer 1. In step (i), the signal analyzer 1 requests the mobile terminal 11 to decrease the transmission power on the basis of the above mentioned TPC of the downlink. In step (m), the mobile terminal 11 decreases the transmission power by the set step size “Ps” to transmit a signal using the decreased transmission power “Pmax-Ps”.
In step (n), the signal analyzer 1 requests the mobile terminal 11 to decrease the transmission power. In step (o), the mobile terminal 11 decreases the transmission power by the set step size “Ps” to transmit a signal using the decreased transmission power “Pmax−2Ps”. Similarly, the mobile terminal 11 decreases the transmission power by the set step size “Ps” with respect to each of the transmission power decreasing requests from the signal analyzer 1, and transmits a signal using the decreased transmission power.
In response to the transmission power decreasing request made in step (p) by the signal analyzer 1, the mobile terminal 11 decreases the transmission power “Pue=Pmax−(n−1)Ps” by the set step size “Ps”, and transmits a signal using the decreased transmission power “Pmax−nPs” in step (q). Here, the character “n” indicates a positive integer and the times of the transmission power decreasing request from the signal analyzer 1.
In step (r), the signal analyzer 1 judges whether or not the transmission power “Pue” of the mobile terminal 11 is smaller than or equal to the minimum value “Pmin” based on the CLPC measurement. As shown in FIG. 13, the signal analyzer 1 determines that “Pue=Pmax−nPs=Pmin”. Although the determinations of each step size are not fully explained in FIG. 13, the signal analyzer 1 makes the determinations of each step size in steps (m) and (o).
In response to this judgment, the signal analyzer 1 requests the mobile terminal 11 to increase the transmission power of the mobile terminal 11 on the basis of the TPC of the downlink in step (s). In response to this request, the mobile terminal 11 increases the transmission power by the set step size “Ps”, and transmits a signal using the increased transmission power in step (t). In this step, the increased transmission power becomes “Pmax+Ps”. In the same way, the mobile terminal 11 increases the transmission power in increments of the set step size “Ps”, and repeatedly transmit a signal using the increased transmission power.
In response to the request made in step (u) by the signal analyzer 1 to increase the transmission power, the mobile terminal 11 increases the transmission power by the set step size “Ps”, and transmits a signal by using the increased transmission power in step (v). In this step, the transmission power “Pue” of the mobile terminal 11 is increased from “Pmax+(m−1)Ps” to “Pmax+mPs”. Here, the natural number “m” indicates the number of the requests made and transmitted from the signal analyzer 1 to the mobile terminal 11 to gradually increase the transmission power.
In step (w), the signal analyzer 1 determines whether or not the transmission power “Pue” of the mobile terminal 11 is larger than or equal to the maximum value “Pmax” based on the CLPC measurement. As shown in FIG. 13, when Pue=Pmin+mPs=Pmax, the signal analyzer 1 terminates the control necessary to increase the transmission power “Pue” of the mobile terminal 11 to the maximum value from the minimum value in increments of the set step size, and to decrease the transmission power “Pue” of the mobile terminal 11 to the minimum value from the maximum value in decrements of the set step size. Although the determinations of each step size are not fully explained and omitted in FIG. 13, the signal analyzer 1 makes the above-mentioned determinations with respect to each step size in step (t).
Additionally, the number “m” is equal to the number “n” under the condition that the transmission power “Pue” of the mobile terminal 11 is changed in increments of an ideal step size as shown in FIG. 14. However, the increased or decreased transmission power of the mobile terminal 11 has a margin of error even if the transmission power “Pue” of the mobile terminal 11 is increased or decreased in decrements of the set step size.
The operation about the test of the CLPC function of the signal analyzer 1 thus constructed will be described hereinafter with reference to FIG. 15. FIG. 15 is a flow chart showing the operation of the conventional signal analyzer 1.
Firstly, the power control setting section 3 outputs, to each part of the signal analyzer 1, information necessary to carry out the test of the CLPC function through the control section 4 on the basis of the information from the power control setting section 3 (in step S1).
Then, the power control request section 5a outputs, to the transmitting circuit 5b, a control signal to control the mobile terminal 11 to set the transmission power of the mobile terminal 11 to a value larger than or equal to the maximum transmission power based on the CLPC standard. In response to the control signal from the power control request section 5a, the transmitting circuit 5b outputs control information corresponding to the control signal to the mobile terminal 11 through the directional coupler 2 and the connecting terminal 1a to set the transmission power of the mobile terminal 11 to a value larger than or equal to the maximum transmission power based on the CLPC standard (in step S2).
In response to the request from the power control request section 5a, the mobile terminal 11 sets the step size of the mobile terminal 11 to 1 dB through the transmitting circuit 5b, the directional coupler 2, and the connecting terminal 1a (in step S3).
In the same way, the power control request section 5a requests the mobile terminal 11 to transmit a signal. In response to the transmission request from the power control request section 5a, the mobile terminal 11 starts to transmit a signal using a maximum transmission power based on the CLPC standard. And the signal starts to be received from the mobile terminal 11 by the receiving circuit 6a, and converted to digital waveform data which are stored in the memory section 6c. At the same time, the slot detecting section 7a starts to reads out digital waveform data from the memory section 6c, and detects a start point of each slot on the basis of the information from the control section 4 or the power control request section 5a. The slot power detecting section 7b detects a transmission power of each slot detected by the slot detecting section 7a, and stores the transmission power of each slot in the analysis result memory section 7c (in step S4). The slot detecting section 7a, the slot power detecting section 7b, and the analysis result memory section 7c perform respective operations to immediately detect transmission powers of slots of all the waveform data stored in the memory section 6c. 
The power control request section 5a requests the mobile terminal 11 to decrease the transmission power by the current step size. The mobile terminal 11 decreases the transmission power by the current step size in response to the request from the power control request section 5a, and transmits a signal using the decreased transmission power (in step S5). Additionally, the transmission power is updated with respect to each slot.
The control section 4 judges whether or not the transmission power of the mobile terminal 11 is smaller than or equal to the minimum transmission power based on the CLPC measurement standard (in step S6). When the transmission power of the mobile terminal 11 is not smaller than or equal to the minimum transmission power based on the CLPC measurement standard (S6-No), the power control request section 5a controls the mobile terminal 11 to further reduce the transmission power of the mobile terminal 11 by the current step size. When, on the other hand, the transmission power of the mobile terminal 11 is smaller than or equal to the minimum transmission power based on the CLPC measurement standard (S6-Yes), the power control request section 5a requests the mobile terminal 11 to increase the transmission power of the mobile terminal 11 by the current step size. The mobile terminal 11 increases the transmission power by the current step size in response to the request from the power control request section 5a, and transmits a signal using the decreased transmission power (in step S7).
Then, the control section 4 judges whether or not the transmission power of the mobile terminal 11 is larger than or equal to the maximum transmission power based on the CLPC measurement standard (in step S8). When the transmission power of the mobile terminal 11 is not larger than or equal to the maximum transmission power based on the CLPC measurement standard (S8-No), the control section 4 controls the mobile terminal 11 to increase the transmission power of the mobile terminal 11 by the current step size (in step S7). When, on the other hand, the transmission power of the mobile terminal 11 is larger than or equal to the maximum transmission power based on the CLPC measurement standard (S8-Yes), the control section 4 judges whether or not the measurement of the transmission power of each slot has been measured in every step size based on the CLPC measurement standard through the process of decreasing the transmission power of the mobile terminal 11 from the maximum transmission power to the minimum transmission power, and increasing the transmission power of the mobile terminal 11 from the minimum transmission power to the maximum transmission power (in step S9). When the measurements of the transmission powers is partially completed (S9-No), the power control request section 5a changes the step size of the mobile terminal 11 to the remaining step size (in step S10). When, for example, the current step size is 1 dB, the power control request section 5a changes the step size to “+2 dB” by increasing the current step size by “+1 dB”.
When all the measurements of the transmission power of the mobile terminal 11 is completed with respect to each step size (S9-Yes), the memory section 6c completes the storing operation after storing all the measured transmission power of each slot, and the analysis result memory section 7c completes the storing operation after storing all the measured transmission power of each slot (in step S11). The display control section 9 reads out the transmission power of each slot from the analysis result memory section 7c, and produces display data necessary to display the transmission powers of slots ordered in time on the display section 10 (in step S12).
FIG. 16 is a graph showing an example displayed on a screen by the conventional signal analyzer. The vertical axis of the graph located in the electric power graph display section 32 is a power scale (the transmission power is measured in decibels with reference to one milliwatt (dBm), and shown without a scale). Here, the stepped graph shows the transmission powers of slots ordered in time. In FIG. 16, the reference character “Sa” indicates a section showing measurement results obtained under the condition that the transmission power of the mobile terminal 11 is decreased in increments of “1 dB”. In the same way, the reference character “Sb” indicates a section showing measurement results obtained under the condition that the transmission power of the mobile terminal 11 is increased in increments of “1 dB”. The reference character “Sc” indicates a section showing measurement results obtained under the condition that the transmission power of the mobile terminal 11 is decreased in increments of “2 dB”. The reference character “Sd” indicates a section showing measurement results obtained under the condition that the transmission power of the mobile terminal 11 is increased in increments of “2 dB”.
Actually, the step size of the mobile terminal is changed to other step size in a period of time intervening between sections “Sb” and “Sc”, and further set in a period of time intervening between sections “Sd” and “Se”. The display control section 9 of the signal analyzer 1 however displays measurement results corresponding to the sections without showing measurement results corresponding to those periods of time.
Although a sign indicating an irregular slot is not shown in FIG. 16, the judging section 8 of the signal analyzer 1 compares the measurement result of each slot and the reference value of the test of the CLPC function. When the judgment is made that one or more measurement results are irregular, the display control section 9 displays a sign indicating an irregular slot.
The operation check of the judging section 8 of the mobile terminal 11 is performed on the basis of, for example, reference tables shown in FIG. 17 or FIG. 18. Those reference tables shows examples of the reference values of the test of the CLPC function, and stored in a memory section (not shown). FIG. 17 is a graph showing an example of the standard table, the first row (1) corresponds to standard values to be used when the transmission power is increased by each of the step sizes 1 dB, 2 dB, and 3 dB, the second row (2) corresponds to standard values to be used when the transmission power is maintained by each of the step sizes 1 dB, 2 dB, and 3 dB, and the third row (3) corresponds to standard values to be used when the transmission power is decreased by each of the step sizes 1 dB, 2 dB, and 3 dB. Here, the reference value of FIG. 17 is indicative of the (relative quantity) difference between the transmission power of the relevant slot and the transmission power of a slot adjacent to the relevant slot.
In the standard value table shown in FIG. 18, the first row (1) shows standard values which are used when the transmission power is increased in increments of 1 dB, 2 dB, or 3 dB, the second row (2) shows standard values which are used when the transmission power is maintained in increments of 1 dB, 2 dB, or 3 dB, and the third row (3) shows standard values which are used when the transmission power is increased in increments of 1 dB, 2 dB, or 3 dB. Here, the reference value of FIG. 18 is indicative of the (relative quantity) difference between the transmission power of the relevant slot and the transmission power of a slot separated from the relevant slot by 10 slots (7 slots corresponds to 3 dB).
For details, refer to for example a patent document 1 explaining the construction of the above-mentioned signal analyzer.
Patent document 1: Japanese Patent Laid-Open Publication 2003-46431